1. Title of the Invention
The present invention relates to a non-contacting power supply system for a rail-guided vehicle, and more particularly to a non-contacting power supply system for supplying electric power to a rail-guided vehicle which moves along a plurality of power supply lines having respective power sources.
2. Description of the Related Art
Conventionally, a non-contacting power supply system for a rail-guided vehicle is frequently arranged by using a power supply line having a maximum length of 100 meters, with a single power source.
However, the demand for arranging a non-contacting power supply system having a longer power supply line, such as a 300-meter line, 500-meter line, etc. has been increasing in recent years, which leads to the use of a plurality of power sources. This is because a single power source has a supply limit.
In the case of an arrangement of a long power supply line, the power supply line is divided into a plurality of sublines, to each of which a power supply unit is connected. The ends of the plurality of sublines are arranged to be as close as possible in consideration of safety, deviation, a temperature change, etc., so as to prevent a power supply from stopping or decreasing to a low level in the portion between two power supply lines.
The frequencies and phases of the power supply units for the plurality of sublines are controlled to be almost the same. If the frequencies and phases of two power supply units are exactly the same, a rail-guided vehicle can properly pass through the portion between the sublines.
Provided below is the explanation about the relationship between the portion between conventional power supply lines and a power receiving core, by referring to FIG. 1.
A power receiving core 1 is wound with an electric wire (a winding 7 to be described later), which receives induced electric power from a power supply line and supplies the received power to the drive system of a rail-guided vehicle.
Power supply lines 2 and 3 are sublines into which one line is divided, and are respectively connected to power supply units 4 and 5.
The power supply units 4 and 5 are units which can output an alternating current with a large power capacity at a high frequency.
A rectifying element 6 is an AC/DC converting element for converting the high frequency electric power, which is received by the power receiving core 1, into a direct current, and for supplying the DC power to the drive system of the rail-guided vehicle.
The winding 7 is a winding for generating electric power by being oriented in the direction which is most susceptible to the electric power from the magnetic flux in the magnetic field generated in both the power supply lines 2 and 3 and by being positioned as near as possible to the portion where the magnetic flux is the strongest.
If the frequencies and phases of the power supply units 4 and 5 for both of the divided power supply lines 2 and 3 are exactly the same and are fully synchronized, electric power can be supplied in the portion obtained by subtracting the length L1 from L2 in the power receiving core 1, although the supplied electric power decreases in the gap L1 between the power supply lines 2 and 3, when the rail-guided vehicle passes between the power supply lines 2 and 3. Therefore, the rail-guided vehicle can properly pass through the portion between the power supply lines 2 and 3.
However, since a power supply line to which a single power supply unit can supply electric power is approximately 100 meters long, the wiring for connecting a plurality of power supply units which are intended to have synchronized phases, can be expected to be longer. Additionally, the device for synchronizing the phases of the plurality of power supply units is newly required, which leads to troublesomeness. Accordingly, a plurality of conventional power supply units do not perform such a process for making the frequencies and phases exactly the same.
Additionally, even if the frequencies of the plurality of power supply units are respectively set to be the same, the actual frequencies may slightly differ from one another due to the differences in operation of the PLLs of the respective power supply units. Because the timing at which the waveforms are outputted from the respective power supply units differ, the phases of the respective power supply units may differ.
When the rail-guided vehicle tries to pass through the portion between power supply lines under such conditions that the frequencies and the phases are different, a beat tone occurs in the supplied electric power due to the difference between the frequencies of the corresponding power supply units. Since the frequency of the beat is much lower than that of the power source, it is approximate to a direct current. Accordingly, the loss of the power source rapidly increases, and an overcurrent occurs inside the power source, so that a protection circuit will operate, a switching element will be destroyed, or the power supply units will become uncontrollable. If there is a difference between the power capacities of the power supply units, the power supply unit with a smaller power capacity will become uncontrollable. If there is almost no difference, both of the power supply units may sometimes become uncontrollable.
If the frequencies are exactly the same, a phase lag only increases the maximum amplitude of an output. However, if the above described beat occurs, the maximum amplitude of the beat will be increased.